Effective scanning resolution enhancement

Abstract

An inspection system to inspect structures on a substrate. A generator directs a primary beam at the substrate along a selectable angle, thereby producing a secondary beam having properties that are characteristic of the structures on the substrate. At least one of the substrate and the primary beam are scanned relative to the other at a selectable speed. A sensor receives the secondary beam and provides analog signals having properties that are characteristic of the secondary beam. An analog to digital converter receives the analog signals and provides digital signals having properties that are characteristic of the analog signals. A controller receives the digital signals and determines the properties of the structures on the substrate based at least in part on the properties of the digital signals.

1. An inspection system adapted to inspect structures on a substrate, the inspection system comprising:
 a beam generator adapted to direct a primary beam at the substrate at a variable scanning angle as defined by X and Y coordinates and not by an angle of incidence of the primary beam on the substrate, thereby producing a secondary beam having properties that are characteristic of properties of the structures on the substrate, 
 a stage adapted to scan the substrate relative to the primary beam at a selectable speed, where a direction of movement of the stage is defined as the X coordinate, and the Y coordinate is perpendicular to the X coordinate within a plane of the substrate, 
 a sensor adapted to receive the secondary beam and provide analog signals having properties that are characteristic of the properties of the secondary beam, 
 an analog to digital converter adapted to receive the analog signals and provide digital signals having properties that are characteristic of the properties of the analog signals, and 
 a controller adapted to receive the digital signals and determine the properties of the structures on the substrate based at least in part on the properties of the digital signals, and to selectively order the digital signals in an output based on a relationship between the variable scanning angle and the selectable speed, where a resolution of the inspection system is variable based on the variable scanning angle and the selectable speed. 
 
   
   
     2. The inspection system of  claim 1 , wherein the variable angle is between about forty-five degrees and about ninety degrees. 
   
   
     3. The inspection system of  claim 1 , wherein the variable angle is about forty-five degrees. 
   
   
     4. The inspection system of  claim 1 , wherein the selectable speed is equal to about cosine of ninety degrees minus the variable angle, times a nominal speed used when the variable angle is ninety degrees. 
   
   
     5. The inspection system of  claim 1 , wherein the secondary beam is a reflected beam. 
   
   
     6. The inspection system of  claim 1 , wherein the substrate is a semiconductor wafer. 
   
   
     7. The inspection system of  claim 1 , wherein the substrate is a mask for an integrated circuit layer. 
   
   
     8. An inspection system adapted to inspect structures on a substrate, the inspection system comprising:
 a beam generator adapted to direct a primary beam at the substrate at an adjustable angle as defined by X and Y coordinates and not by an angle of incidence of the primary beam on the substrate, thereby producing a secondary beam having properties that are characteristic of properties of the structures on the substrate, 
 means for adjusting a selectable angle at which the primary beam scans on the substrate, 
 a substrate stage adapted to hold the substrate underneath the primary beam, where a direction of relative movement between the stage and the primary beam is defined as the X coordinate, and the Y coordinate is perpendicular to the X coordinate within a plane of the substrate, 
 means for scanning at least one of the substrate and the primary beam relative to the other at a selectable speed, 
 an input adapted to receive the selectable angle and the selectable speed, 
 a sensor adapted to receive the secondary beam and provide analog signals having properties that are characteristic of the properties of the secondary beam, 
 an analog to digital converter adapted to receive the analog signals and provide digital signals having properties that are characteristic of the properties of the analog signals, and 
 a controller adapted to adjust the selectable angle, adjust the selectable speed, receive the digital signals, and determine the properties of the structures on the substrate based at least in part on the properties of the digital signals, and to selectively order the digital signals in an output based on a relationship between the variable scanning angle and the selectable speed, where a resolution of the inspection system is variable based on the variable scanning angle and the selectable speed. 
 
   
   
     9. The inspection system of  claim 8 , wherein the beam is a laser beam. 
   
   
     10. The inspection system of  claim 8 , wherein the selectable angle is between about forty-five degrees and about ninety degrees. 
   
   
     11. The inspection system of  claim 8 , wherein the selectable angle is about forty-five degrees. 
   
   
     12. The inspection system of  claim 8 , wherein the selectable speed is equal to about cosine of ninety degrees minus the selectable angle, times a nominal speed used when the selectable angle is ninety degrees. 
   
   
     13. The inspection system of  claim 8 , wherein the substrate is a semiconductor wafer. 
   
   
     14. The inspection system of  claim 8 , wherein the substrate is a mask for an integrated circuit layer. 
   
   
     15. The inspection system of  claim 8 , wherein the secondary beam is a reflected beam. 
   
   
     16. A method to inspect structures on a substrate, the method comprising the steps of:
 directing a primary beam at the substrate at a selectable angle as defined by X and Y coordinates and not by an angle of incidence of the primary beam on the substrate, thereby producing a secondary beam having properties that are characteristic of properties of the structures on the substrate, 
 scanning at least one of the substrate and the primary beam relative to the other at a selectable speed and in a direction, where the selectable angle is not ninety degrees relative to the direction, where the direction is defined as the X coordinate, and the Y coordinate is perpendicular to the X coordinate within a plane of the substrate, 
 receiving the secondary beam and providing analog signals having properties that are characteristic of the properties of the secondary beam, 
 receiving the analog signals and providing digital signals having properties that are characteristic of the properties of the analog signals, 
 determining the properties of the structures on the substrate based at least in part on the properties of the digital signals, and 
 selectively ordering the digital signals in an output based on a relationship between the variable scanning angle and the selectable speed, where a resolution of the inspection method is variable based on the variable scanning angle and the selectable speed. 
 
   
   
     17. The method of  claim 16 , wherein the primary beam is a laser beam. 
   
   
     18. The method of  claim 16 , wherein the secondary beam is a reflected beam. 
   
   
     19. The method of  claim 16 , wherein the selectable angle is about forty-five degrees.